a-short-review-of-histology

The Pituitary Gland - Development:

The posterior pituitary, or neurohypophysis, is composed of the axons of non-myelinated neurons and pituicytes, or support cells
Like the anterior pituitary, there are numerous fenestrated capillaries lying between the parenchymal cells
The axons of the posterior pituitary cells terminate on the capillaries
The axons which are found in the posterior pituitary pass through the pituitary (neural) stalk which connects to the hypothalamus
The axons are from neuronal cell bodies located in the para-aortic and paraventricular nuclei within the hypothalamus of the brain
In the central nervous system a nucleus is the term given to a collection of neuronal cell bodies
The posterior pituitary produces two hormones, antidiuretic hormone and oxytocin
These hormones are produced within the cell bodies of the neurons in, respectively (mainly), the supra-optic and paraventricular nuclei
They are passed along, within membrane bound vesicles, the axons which themselves pass down through the neural stalk and into the posterior pituitary
When neurons in the hypothalamus are triggered to release hormone, an action potential passes along the axon and stimulates exocytosis of hormone from the axon ending: the hormone then diffuses into capillaries
At the nerve ending, the collections of hormone containing vesicles can be quite large and may be visible in histological preparations; they are sometimes known as "Herring bodies"

Micrograph of Posterior Pituitary:

This micrograph shows the typical appearance of a histological preparation of posterior pituitary
The nuclei are mainly from the pituicytes which support the axons that have passed down the neuronal cell bodies in the hypothalamus
Note the large diameter thin walled capillaries [C] that are typical of the pituitary gland
Adjacent to one capillary lies a swollen nerve ending (arrow) containing vesicles of hormone
Such swellings of nerve endings are known as "Herring bodies"